1. Anesthesia Monitoring and Equipment
Simeneh Mola (Bsc, Msc)
DU, Department Of Anaesthesia
September, 2018

2. Anesthesia Equipments
Medical Gas supply
Anaesthetic machine
Breathing systems
Humidification and filtration
Airways
Tracheal intubation equipment
Masks and oxygen delivery devices
Ventilators

3. MEDICAL GAS SOURCES

4. A brief overview of relevant gas physics
N / m2
(Pa)
Pressure = force
area m2
What is the relationship between pressure, temperature and volume?
Universal gas constant
(8.314 N / m2.mole.K)
Pressure (Pa)
PV = nRT
Temperature (Kelvin)
Volume (m2)
Number of moles of gas
This is the “Universal Gas Law”

5. Cont’d PV = nRT (The Universal Gas Law) So;
Doubling the temperature of a fixed amount of gas in a fixed volume
will double the gas pressure
Doubling the temperature of a fixed amount of gas at a certain pressure
will double the volume

6. The “Universal Gas Law” ; PV = nRT
A practical example:
A size E oxygen cylinder has 5 L of compressed O2 at a pressure of kPa
What is the volume of O2 at atmospheric pressure (101 kPa)?
Assuming the gas temperature is the same at start and finish;
P1V 1 = P2V2
So, V2 = P1V1 / P2
= kPa.V1 / 101 kPa
= 135 X 5 L
≈ 680 L
(the volume of O2 expected from a full size E cylinder)

7. Different unit of pressure
Psi- pound per square inch
Psig- pound per square inch gage
Psia - pound per square inch absolute
Conversion factor
100kpa= 1 bar= 760 mmHg = cmH2o= 14.7 psi = 1 atm

8. Main Gases used in anaesthesia
Essential for almost all general anaesthesia; physiological changes during GA mean patient requires higher FiO2
Oxygen
Air
Preferable to avoid excessive FiO2 if possible (requires judgment)  excessive FiO2 causes lung damage and decreases post-operative respiratory function
N2O
Variable use by anaesthesiologists. Used particularly for smooth gas inductions and for intra-operative analgesia by some.

9. Cylinders, Hospital piping system, or Oxygen concentrator.
Medical gas sources
Cylinders,
Hospital piping system, or
Oxygen concentrator.

10. Medical gas supply How are they supplied? Cylinders in theatre Oxygen
Cylinder manifold (piped to theatre)
Oxygen concentrator
Piped to theatre
To fill cylinders
Directly at bedside
Vacuum insulated evaporator (piped to theatre)
Oxygen
Cylinders in theatre
Directly from air compressor (via wall pipes)
Air
Cylinders in theatre
Cylinder manifold (piped to theatre)
N2O

11. Types of compressed Gas
Nonliquefied Compressed Gas
Gas that does not liquefy at ordinary temperatures regardless of the pressure applied.
Examples include O2, N, Air, and He.
Liquids at very low temperatures (cryogenic liquids)
Liquefied Compressed Gas
Gas that becomes liquid to a large extent in containers at ambient temperature and at pressures from 25 to 1500 psig.
Examples include N2O & CO2.

15. Oxygen Cylinders

16. Components
Consists of:
Body
Valve
Port
Stem
Pressure relief devices

17. Most medical gas cylinders are made of steel with various alloys added
Body:
Most medical gas cylinders are made of steel with various alloys added
In recent years, manufacturers have moved from traditional steel cylinders towards steel-carbon fibers cylinders
MOLYBDENUM + STEEL +/- CHROMIUM Alloy containing Molybdenum ( %) Chromium (If %) 
Can hold more gas and light in weight

18. Valve:
Cylinders are filled and discharged through a valve (spindle shaped) attached to the neck
It is made of bronze or brass which is heavily plated with nickel or chromium so as to allow rapid dissipation of heat of compression
The end which enters the neck of the cylinder is threaded to fit a corresponding screw thread inside the neck itself

20. Port:
It is the point of exit for the gas
It fits into the nipple on the hanger yoke of the anesthesia machine
It should be protected in transit by a covering
When installing a cylinder on anesthesia machine, it is important for the user not to mistake the port for the conical depression

22. Conical depression
is situated on the opposite side of the port on the cylinder valve and is situated above the safety relief device
It is present on those cylinders which are designed to fit on anesthesia machine
Conical depression is designed to receive the retaining screw on the yoke of the anesthesia machine
Screwing the retaining screw into the port may damage the port

24. Pressure Relief Devices:
Every cylinder is fitted with pressure relief devices whose purpose is to vent the cylinder’s contents to the atmosphere if the pressure of enclosed gas increases to dangerous levels
Types:
• Rupture Disc
• Fusible Plug
• Combination of Both
• Pressure Relief valve (spring loaded)

25. Rupture Disc:
• When pre-determined pressure is reached the disc ruptures and allows the gas contents to be discharged
• It is a non- reclosing device held against an orifice
• It protects against excess pressure as a result of high temperature/overfilling

27.  Fusible Plug:
• It is thermally operated
• It is a non-reclosing pressure relief device where the plug is held against the discharge channel
• It provides protection against excess pressure due to high temperature but not overfilling
• YIELD TEMPERATURE: Temperature at which fusible material becomes sufficiently soft to extrude from its holder- so that cylinder contents are discharged

28. Spring loaded pressure relief device:
• It is a reclosing device
• When set pressure is exceeded, the pressure in the cylinder forced the spring to open the channel for letting out the gases Gas flows around the safety valve seat to discharge channel till excess pressure is relieved

29. Cont’d
When the set pressure is exceeded, the pressure in the cylinder forces the spring to the left, and gas flows around the safety valve seat to the discharge channel.

30. How is the pressure reduced?
Pressure reduction valves:
These supply gases to the anaesthetic machine at about 4 Bar (or 400 kPa)
Low Pressure Out
High Pressure in

31. Pin index safety system
Consists of holes on the cylinder valve positioned in an arc below the outlet port.
Unless the pins and holes are aligned, the port will not seat.
It is possible for a yoke or pressure regulator without pins to receive any cylinder valve, but it is not possible for an undrilled cylinder to be placed in a yoke or regulators containing pins .

32. Cont’d Oxygen 2, 5 Nitrous Oxide 3, 5 O2-CO2 (CO2 < 7.5%) 2, 6
Gas
Index Pins
Oxygen
2, 5
Nitrous Oxide
3, 5
O2-CO2 (CO2 < 7.5%)
2, 6
O2-CO2 (CO2 > 7.5%)
1, 6
O2-He (He > 80.5%)
4, 6
O2-He (He < 80.5%)
2, 4
Air
1, 5
Nitrogen
1, 4
N2O-O2 (N2O 47.5%–52.5%) 7
Cyclopropane
3, 6

33. Cont’d
Pin index system works well for the common gases used in anesthesia.
There are problems when specialized gas mixtures are used.
As an example, a 5% CO2 mixture with oxygen has a different pin index than 100% carbon dioxide.
Carbon dioxide mixtures of 7% or greater CO2 would be fitted with the pin index of 100% CO2.

34. Cont’d

35. Size Classified cylinders using a letter code A begin the smallest
E is the cylinder most commonly used on anesthesia machines.
The volume and pressure of gas in a particular size cylinder vary.
O2 and air are similar in volumes and pressures.
True for CO2 and N2O.
Cylinder size
Capacity
Pressure/psig B
200
1900 D
400 E
660 M
3450
2200 H
6900

36. Contents and pressure
In cylinder containing a non liquefied gas the pressure declines steadily as the contents are withdrawn, therefore, the pressure can be used to measure the cylinder contents. (What else???)
In cylinder containing a liquefied gas, the pressure depends on the vapor pressure of the liquid and is not an indication of the amount of gas remaining in the cylinder as long as the contents are partly in the liquid phase. (so how could u measure it???)

38. Cont’d
A: A gas stored partially in liquid form, such as nitrous oxide, will show a constant pressure (assuming constant temperature) until all the liquid has evaporated, at which time the pressure will drop in direct proportion to the rate at which gas is withdrawn.
B: A nonliquefied gas such as oxygen will show a steady decline in pressure until the cylinder is evacuated. Each cylinder, however, will show a steady decline in weight as gas is discharged.

39. Testing
A cylinder must be inspected and subjected to internal hydrostatic pressure testing at least every 5 years or with special permit up to every 10 years.
The test (month and year) must be permanently stamped.
Strength by testing to a minimum of 1.66 (1.5 in Canada) times their service pressure.
A cylinder that leaks or expands more than the allowable limit must be rejected.

40. Color Used as a means to aid in identifying gases in use.
The top and shoulder of each cylinder are painted the color assigned to the gas it contains.
An international color code has been adopted.
Is useful to identify the contents of a cylinder from a distance.
Gas
International O2
White
CO2
Gray
N2O
Blue He
Brown N2
Black
Air
White & black
Color should be not be used as the primary means for identification of cylinder contents.
Cylinder labels are the best method .

41. Markings Regulations require specific markings on each cylinder.
Permanently stamped, usually onto the shoulder of the cylinder.
The markings of a typical cylinder might be arranged horizontally as follows:
Specification
Service pressure (at 70°F)
Serial number
Manufacturer
Owner's symbol
3A2015
8642
XYZ
JCN

42. Question What does the following marking means? 3AA1900 13730
Moha soft drink factory
DUR Hospital

43. Labeling Should contain Name and address of the cylinder manufacturer,
Statement about its content,
Volume in liters at 70°F,
Cylinder weight when empty and full,
The expiratory date.

44. Tags
It has three sections
EMPTY,
IN USE, and
FULL
When a cylinder is put into service, the FULL portion of the tag should be detached. When the cylinder is empty, the IN USE portion should be removed, leaving the EMPTY label.
Primarily a means of denoting the amount of cylinder contents, not an identification device.

45. General rules for safe use of cylinders
Should be handled only by trained personnel.
Valves, pressure regulators, gauges, or fittings should never come in contact with oils, greases, organic lubricants, rubber.
No part of any cylinder should ever be subjected to a temperature above 54°C (130°F) or below -7°C (20°F). Why??
Connections to d/t equipments should always be kept tight to prevent leaks.
Pressure relief device or the valve outlet must not be obstructed.

46. Cont’d
Adapters to change the outlet size of a cylinder valve should not be used. Why???
The valve should be kept closed at all times except when the cylinder is in use. No more force to close.
No part of the cylinder or its valve should be tampered with, painted, altered, repaired, or modified by the user.
Markings, labels, or tags must not be defaced, altered, or removed.
A cylinder should not be used as a roller, support, or for any other purpose.

47. Cont’d
Cylinders not be placed or used in a manner where they can become part of an electrical circuit.
Cylinders should not be dropped, dragged, slid, or rolled, even for short distances.

48. Cont’d
The owner of the cylinder must be notified if any damage is noticed.
Disposition of unserviceable cylinders should be done only by qualified personnel.
Cylinders should be properly secured at all times to prevent them from falling or being knocked over.

49. Storage A definite area should be designated (Not OR).
The storage area should be in a cool, dry clean, well- ventilated room that is constructed of fire-resistant material.
Easily visible signs with texts such as:-
“GAS CYLINDERS”
“REMOVE TO A SAFE PLACE IN THE EVENT OF FIRE”
“OFF LIMITS TO UNAUTHORIZED PERSONNEL”
“NO SMOKING,”
“NO OPEN FLAMES OR SPARKS,”
“NO OIL OR GREASE,” and
“NO COMBUSTIBLE MATERIALS”

50. Cont’d Should be protected against extremes of weather.
Cylinders should be stored in a secure area.
Combustible materials should not be kept near cylinders (with rare exceptions).
Cylinders should be protected from mechanical shock.
Small cylinders are best stored upright or horizontally while Large cylinders should be stored upright against a wall and chained in place.
There should be a system of inventory for both empty and full cylinders.
Wrappings…

51. Use
Before use the content of the cylinder should be identified. How???
A pressure regulator should always be used.
Before a regulator is connected to a cylinder, it should be inspected for signs of damage and FB.
Before any fitting apply slow and brief opening (“cracking”) of the valve.
Protection cap should be removed just before connecting.
Connectors that do not fit should never be forced.

52. Cont’d
The person opening a cylinder valve should position himself or herself… & goggles.
A cylinder valve should always be opened SLOWLY ?
After the cylinder valve is opened, the pressure should be checked.
Cylinder must be secured to a cylinder stand or to apparatus of sufficient size to render the entire assembly stable.
The valve should always be fully open when a cylinder is in use.

53. After use Valve should be closed.
An empty or near-empty cylinder should not be left on an anesthesia machine. Why???
Before removing a cylinder the valve should be closed and all downstream pressure released.
Valves should be completely closed on all empty cylinders.???
Valve protection caps should be replaced before shipment.

54. Oxygen concentrators

55. Mechanism
Depends on the property of an artificial Zeolite to entrap molecules of nitrogen.

56. Advantages Cost Savings - $ Contaminant Filtration
Compatibility with Most Gas Monitors - Argon
Reliability – attitude changes
Simplicity

57. Disadvantages Maintenance – filter change
Less Than 100% Oxygen Produced – max...
Fires Hazards – overheated, tube rub…
Water Contamination – very high humidity
Contaminated Intake Air – premature exhaustion
Device Malfunction – restricted flow to it, kink, run but no…
Argon Accumulation – max 5%, problem if 0.5L/m, no pt effect

58. Anesthesia Equipments
Medical Gas supply √
Anaesthetic machine
Breathing systems
Humidification and filtration
Airways
Tracheal intubation equipment
Masks and oxygen delivery devices
Ventilators